1. Field of the Invention
The present invention relates to medical catheters and guidewires commonly used in the placement of catheters in a patient's vascular system, and particularly to infusion wires that can be used either as a guidewire or an infusion catheter.
2. Description of the Background Art
Medical catheters and guidewires are devices that can be navigated through narrow body passages, typically blood vessels, until the distal end section is in a desired location. Guidewires are typically used for introduction of a catheter over the guidewire.
Cardiovascular guidewires typically have a solid core wire and are dimensioned to be received within a catheter lumen as the catheter is advanced over the guidewire. One very common guidewire construction has an elongated, flexible, helical coil having a proximal end and a distal end, the latter being inserted into the patient's vascular system. The internal core wire typically extends through the coil lumen with the proximal and distal ends of the core wire attached to the proximal and distal ends of the coil. A physician controls the advancement and resulting position of the distal end of the guidewire by manipulations performed at the proximal end outside the body. Then, a catheter is advanced over the guidewire, which may be left in place or withdrawn during a procedure using the guidewire.
In order to advance the catheter over the guidewire, it must be uniform in outer diameter or have only step down diameter reductions and no diameter increases. In addition, both catheters and guidewires are preferably constructed with radiopaque markers that are have greater radiopacity and hence higher visibility under fluoroscopy than the bulk of the elongated catheter or guidewire body. These markers allow the physician to visualize the location of the distal end and/or intermediate point(s) along the elongated body within the patient's body. When both the guidewire and the catheter are provided with such markers, care must be taken that they are not so long on one or both device that they mask one another or are confusing. In this regard, it may not be desirable to make the entire wire coil in the distal segment or portion of a high density radiopaque material, because its bright appearance under fluoroscopy would mask any radiopaque marker(s) on the catheter being introduced over it.
Some guidewires are constructed of wire coil defining a guidewire lumen with an outer sheath surrounding or within the wire coil and are adapted for use both as guidewires and as infusion catheters as disclosed, for example, in U.S. Pat. Nos. 5,178,158, 5,184,627, and 5,211,636. They are provided with either a distal axial open end hole or a closed distal end with infusion side holes and a lumen for conveying infusion fluids or body fluids between the proximal end and the end hole or side holes.
In order to operate as a guide wire and be advanced through a tortuous vascular pathway to a desired infusion site, it is necessary that the overall outer diameter be as small as possible and that the construction provide for ease of advancement and excellent steerability or torqueability from the manipulated proximal end to the distal end thereof. Moreover, the construction typically requires increasing flexibility in the intermediate and distal sections. In order to provide adequate infusion capabilities, the side wall thickness has to be minimized to maximize potential infusion volume. The side wall construction also has to withstand high fluid pressures during infusion.
In use, because of the narrow gauge, flexibility and column strength, the distal portion of an infusion guidewire can be advanced to a desired site in a blood vessel. Then, the physician can advance a catheter over the infusion guidewire to the site. Depending on the design, the physician can remove the infusion guidewire from the catheter lumen or leave it in place while conducting a procedure with the catheter. Drugs or agents can be infused from the proximal end of the infusion guidewire, through the lumen, and out through the distal end lumen opening or through side holes in the sheath or through spaces between exposed turns of distal wire coil, if any, during or following the procedure using the catheter. Alternatively, distal blood pressure may be monitored through a fluid column in the lumen.
A further infusion guidewire is disclosed in U.S. Pat. No. 5,322,508 wherein a partial length core wire is attached at the distal end of a metal hypotube guidewire body and extends distally within a wire coil also attached at the distal end of the hypotube. Hypotube construction without a full length core wire may provide a maximal size cross-section, infusion lumen that may accommodate a relatively high infusion flow rate. However, the constriction at the attachment to the distal core wire extension before the distal infusion side holes negates the advantage imparted by the unobstructed hypotube lumen. Moreover, hypotube does not provide for a 1:1 torque transmission down the length of the guidewire during twisting or rotational advancement.
Currently, there are two types of clinically used infusion guidewires, one having a closed end of the type disclosed in the '627 patent and another having an open end of the type disclosed in the '158 patent and sometimes referred to as a "convertible wire". The '158 and '627 patents describe infusion wires and convertible wires having full length, coiled wire bodies within outer sheathes with constant diameter infusion lumens. In each case, the proximal sections have a polyimide tube between the wire coil and the outer sheath to strengthen that section and allow increased infusate pressure. The convertible wire disclosed in the '158 patent delivers the infusate through a distal end hole of the infusion lumen. The infusion wire disclosed in the '627 patent has a closed distal end and a plurality of infusion side holes cut in the outer sheath which covers the wire coil. In both cases, the removable core wire supplies sufficient column strength for steerability as the convertible wire or infusion wire is advanced to the treatment site.
In use of these infusion wires and convertible wires, when infusion therapy is desired, the core wire must be completely removed, since it occupies the bulk of the infusion lumen and would increase flow resistance and decrease flow rate dramatically were it left in place. The handling of this core wire is bothersome to many physicians. In addition, because of the full length coil construction (and non-attached core wire), it has no steerability or torqueability once the core wire is removed. Physicians may desire to steer the distal end into another vessel after the infusion wire is already deployed. Without the ability to steer the tip, they often will be forced to withdraw the entire convertible wire, then place a regular guidewire at the desired site, follow it with an infusion catheter advanced over the guidewire, and then remove the regular guidewire and replace it with the infusion wire.
While the '636 patent discloses an integral core wire within the infusion lumen of an infusion wire, the depicted embodiments all have at least one full length outer wire coil and a coaxial sheath leaving a small cross-section area for the infusion of infusate at slow, steady rates. A high pressure drop is effected along the length of the guidewire so that the slow infusion rate between the distal coil wire turns and the infusion pressure is relatively insensitive to the fluid pressure of the fluid entering the lumen at the proximal end.
With respect to radiopaque markers, the '627 patent depicts a typical band shaped marker that abuts the distal end of an inner sheath and lies over the continuous inner core wire. The band shaped marker causes a stiffening of the infusion wire body at that point. A further U.S. Pat. No. 4,538,622 depicts a short radiopaque coil wound into the turns of a less radiopaque guidewire coil and the use of brazing to fill the coil turns and the gap with the core wire to hold it in place. The resulting mass is stiff and causes the guidewire to be stiffer along the brazed length than adjacent proximal and distal lengths which in turn negatively affects guidewire performance.
An infusion wire with improved steerability and retaining a high infusion flow rate would therefore be a great improvement. Moreover, in infusion wires of the types described and in other guidewires and catheters, improved radiopaque markers that do not increase the outer diameter or restrict the infusion lumen would also be a great improvement.